22 octubre de 2010 - The emergence of highly pathogenic avian influenza (H5N1 HPAI) has wreaked havoc in avian (domestic and wild) and human populations. According to the World Health Organization, since 2003, H5N1 HPAI has killed 302 people, including 20 so far this year. It is estimated that more than 250 million infected domestic poultry have been culled in Southeast Asia. For the most part, H5N1 HPAI has been held in check by early detection, early reporting, rapid response, improved disease surveillance, better husbandry practices, poultry vaccinations, and other disease mitigation measures, but still, so far this year, 16 countries report viral outbreaks in poultry.

In 1996, H5N1 HPAI was isolated from a domestic goose in China’s Guangdong Province. To the northwest, on Qinghai Lake, China’s largest inland body of salt water, more than 100,000 migratory birds descend every summer to breed or rest during their northern spring migration. Interestingly, the single largest wild bird mortality event attributable to H5N1 HPAI occurred here in 2005, when more than six thousand wild birds died at Qinghai Lake —roughly 50 percent of birds that died were bar-headed geese. Several other large scale mortality events have been reported from this virus, primarily in Russia, but in more recent years, mortality events are in the tens to hundreds of birds, rather than in the thousands which is what typically occurs when this virus is initially introduced into wild bird populations.

Given that H5N1 HPAI is able to infect animals and humans and is not likely to be eradicated in the near future, researchers and scientists need a better understanding of domestic and wild bird distributions, ecosystem and habitat use, daily movements, longer migration routes, as well as husbandry practices, animal farming, trade and marketing systems, and points of contact between wild birds, livestock and people. Much of this information can be feasibly obtained through field investigations and technological applications. To illustrate this point, for example, GPS data collection on migration pathways is used to explore the relationships between different groups of birds and their interactions with domestic fowl in varied agro-ecological landscapes devoid of human observers.

In an effort to pinpoint the role that wild birds play in transboundary disease transmission along major migratory flyways, a team led by the Food and Agriculture Organization of the United Nations (FAO) and the United States Geological Survey (USGS) has to date mounted GPS transmitters on more than 525 waterfowl from 24 species in 11 countries to track their migration by satellite. This and other investigations began after H5N1 HPAI swept the region in 2005 and beyond.

Team researchers now know that the majority of bar-headed geese tagged at Qinghai Lake spend their winters in the Lhasa region of Tibet or further south in India. In these wintering grounds, wild birds have exposure to domestic poultry and potentially, farmed wild birds; and since H5N1 HPAI outbreaks have been reported here, this could be an indication of a dissemination pathway for the virus to move among wildfowl and captive birds, eventually being carried to places along migration routes.

If this is so, wild waterfowl on the eastern portion of the Central Asian Flyway may in fact be helping spread H5N1 HPAI into Mongolia each spring as they move across the Qinghai-Tibetan plateau to the north and east. Most interesting is that this repeatable pattern of wild bird outbreaks at the northern end of their migration pathway each spring does not appear to be occurring in other major flyways, thus demonstrating the complexity surrounding the role of wild birds in the disease epidemiology. In view of this, funding for this type of field research will continue to be important so long as the virus remains persistent and endemic in certain countries, which in turn help spur fears that the virus could mutate into a more transmissible form among humans.